I'd say the main problem is that housing in Canada (and the liberal capitalist world more generally these days) is governed by twin forces that cannot be rationally accommodated without much stricter zoning than we currently have - emotion and investment. Investment is self-evident but by emotion I mean this idea that people have a right to live on an acre of property in a sprawling suburb because "that's what they want." Now, in a heavily-regulated market (such as the suburban markets of the 1950s-1980s), this is doable because government will subsidize and enforce "livable" suburbs (ie. suburbs that have decent access to strip malls, wide roads and cheap credit to ensure a steady stream of buyers). Today, we no longer have the same subsidies and the result has been that the only way the suburban dream can continue is if we allow cities like Brampton to engage in horrendously anti-urban, anti-environmental and, fundamentally, anti-social practices. Now I don't think we need to take away the ability to choose where people want to live but the existing system doesn't accommodate choice in housing imo.
If Brampton's ability to sprawl continuously was curtailed, property values would skyrocket and cheap sprawl would, obviously, become impossible. This is where the issue of investment comes in. Once again, outside of a heavily regulated market, investment practices in housing work toward generating value on the land, regardless of its use value for humans. Look at how much empty plots of land (hell, contaminated land oftentimes) sell because it is within a 15 min walk to downtown Toronto (something we can all agree is going to be a good investment). In the contexts of a suburban city like Brampton, what value would there be in high priced land? The city is on the periphery of the GTA and is around 45-1 hour from downtown Toronto (the main driver of growth in the region, and certainly the most concentrated). Transit is lacklustre (and yes, before I get jumped on, Brampton Transit is great for a suburban city but let's not pretend Brampton has a super fancy transit system either), there isn't a clearly concentrated centre of commerce and jobs (Downtown Brampton doesn't strike me as a particularly thriving urban centre right about now) and the existing built form will perpetuate life styles and patterns of growth that rely on cheap land and cheap credit - how do you densify cul-de-sacs and winding neighbourhoods of SFHs when the built form is hostile to increased density and those living there are somehow still more hostile? When that cheap land dries up, the investment that was going into suburban sprawl isn't going to shift to densifying downtown Brampton, it's going to shift elsewhere. Some will remain but most will be invested into sprawl elsewhere or will be shifted into profitable enterprises - such as the high value urban centres that already exist and have the resources and infrastructure in place to facilitate capital investment. Certainly we can argue whether Brampton will make the shift when it runs out of land - Mississauga is but it's not going easily. My point is also that just cutting off suburban sprawl in Brampton doesn't solve anything. Shifting investment to Toronto only ruins Brampton right now.
So we're then faced with a dilemma. We live in an ostensibly free society, so why should we restrict the ability of people to own a home in Brampton? If you have money, you're entitled to spend it on legal pursuits and owning property isn't illegal. We can restrict people's ability to spend their money (as we have reasonable limits on our freedoms, unlike a certain dysfunctional neighbour) but doing so not only undermines an important mythos for Canadians but it also undermines the vitality of many suburban cities that have grown up over the last 50-60 years on cheap land and cheap credit. And just suggesting that investment should and can shift to Toronto is too simple. Sure, that'll help, but because property is seen as an investment in Toronto by a significant share of the market (perhaps even a majority), increased density will only drive up property values and drive up the costs of living in Toronto. If the last 10-15 years of condo boom have shown us anything, increasing supply doesn't drop property values - not unless the market collapses and that's not in the interests of developers, property owners or renters. Everyone suffers if the market crashes. Also, ruining Brampton to stop suburban sprawl makes sense if we just examine the numbers behind it (farmland saved by preventing sprawl, reductions in greenhouse gases from reduced auto use etc.) but it ignores the fact that Brampton is a city of 100s of thousands who either made a choice that was given to them freely by government or, in some cases, a choice they didn't have (the phenomenon of 3 hour commutes because inner city and inner suburban housing is too expensive).
Personally I think the solution is to make housing a right and to ensure that every person in Canada is guaranteed a place to live. Obviously that's an incredibly complicated and difficult proposition but it would solve the current issues in housing. If you take housing out of the market, you can regulate the cost of units and rationally allocate where housing should go. Instead of hoping that developers will cut into their profit margins to built 5-15 storey buildings, just build them. Once investment housing is no longer the norm, people can choose more freely where they want to live. Those who want the urban experience can move to the city. Those who want the in-between experience can live in "missing middle" housing. Those who want the suburban lifestyle can choose to live in the suburbs. Obviously there would have to be some restrictions but if you can pick and choose between housing styles that have pros and cons, regardless of your income, I think we could reduce some of the demand on inner city and suburban housing (as a decent chunk of it is being driven by cost considerations - either those living in shoebox condos or 3 hour commute suburbia).
Edit* tl/dr, Housing is really complicated and just saying Brampton shouldn't sprawl is too simple an answer (even if it's the right response environmentally and urbanistically). But I think we can have our cake and eat it too lol
